A miniature pH sensor suitable for continuous in vivo monitoring and other biomedical, clinical and analytical applications is to be fabricated and evaluated in vitro first, then in animals. Palladium-palladium oxide in wire form is used as the pH sensing electrode. Experimental data obtained show this Pd-PdO electrode is pH sensitive and is applicable in physiological media. The developing sensor is sufficiently small to be suitable for many biomedical and clinical applications. In vitro evaluation will include studying the effects of variables in the fabrication process on the performance of the sensor. Also, the sensitivity, stability, temperature coefficient, durability and transient response of the Pd-PdO miniature pH sensor will be determined. Preliminary animal studies will be carried out to determine the pH response of the sensor compared to the pH values in vivo. The proposed sensor will find applications in many biomedical and clinical settings.